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From "Lu, Boying" <Boying...@emc.com>
Subject RE: How to paginate through all columns in a row?
Date Mon, 03 Mar 2014 10:57:36 GMT
Thanks a lot for your help.

I use composite column, so I have to change a little bit.
I need to use CompositeRangeBuilder.greaterThan(Object) and lessThenEquals(Object) to ‘get
next page’,
since the API document says little about these APIs,  can I use the String object that represents
the last column as the argument of the greaterThan(Object)?

Thanks again

Boying

From: Theo Hultberg [mailto:theo@iconara.net]
Sent: 2014年2月28日 14:39
To: user@cassandra.apache.org
Subject: Re: How to paginate through all columns in a row?

You can page yourself using the withColumnRange method (see the slice query example on the
page you linked to). What you do is that you save the last column you got from the previous
query, and you set that as the start of the range you pass to withColumnRange. You don't need
to set an end of a range, but you want to set a max size.

This code is just a quick rewrite from the page you linked to and I haven't checked that it
worked, but it should give you an idea of where to start

ColumnList<String> result;
int pageSize = 100;
String offset = Character.toString('\0');
while (true) {
  result = keyspace.prepareQuery(CF_STANDARD1)
   .getKey(rowKey)
   .withColumnRange(new RangeBuilder().setStart(offset).setMaxSize(pageSize).build())
   .execute().getResult();
  while (result.hasNext()) {
    Column<String> col = result.next();
    // do something with your column here, then save
    // the last column to use as the offset when loading the next page
    offset = col.getStringValue();
} while (result.size() == pageSize);

I'm using a string with a null byte as the first offset because that should sort before all
strings, but there might be a better way of doing. If you have non-string columns or composite
columns the exact way to do this is a bit different but I hope this shows you the general
idea.

T#


On Thu, Feb 27, 2014 at 11:36 AM, Lu, Boying <Boying.Lu@emc.com<mailto:Boying.Lu@emc.com>>
wrote:
Hi, All,

I’m using Netflix/Astyanax as a java cassandra client to access Cassandra DB.

I need to paginate through all columns in a row and I found the document at https://github.com/Netflix/astyanax/wiki/Reading-Data
about how to do that.

But my requirement is a little different.  I don’t want to do paginate in ‘one querying
session’,
i.e. I don’t want to hold the returned ‘RowQuery’ object to get next page.

Is there any way that I can keep a ‘marker’ for next page, so by using the marker,
I can tell the Cassandra DB that where to start query.
e.g.  the query result has three ‘pages’,
Can I build the query by giving a marker pointed to the ‘page 2’ and Cassandra will return
the second page of the query?

Thanks a lot.

Boying


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